Data Set Overview
  =================
    This dataset contains astrometric data for eleven Saturn
    satellites. The data were obtained using the HST/WFPC2 over the
    period 1994-2002. The volume contains only derived products.
     PI:       Richard G. French (Wellesley College)
 
 
  Objectives
  ==========
    The observations from which these results were derived were part
    of a long term investigation of Saturn's rings prior to Cassini's
    arrival in 2004. The primary intent of this specific portion of
    the investigation was to refine orbital information for Prometheus
    and Pandora. Observations made during the 1995-1996 Saturn Ring
    Plane Crossing led to the unexpected finding that the positions of
    both satellites varied significantly from the predictions based on
    the Voyager observations (BOSH&RIVKIN1996, NICHOLSONETAL1996,
    MCGHEEETAL2001, SYNNOTTETAL1983). Sufficient observations to
    produce astrometrically meaningful data for nine other satellites
    were obtained incidentally in the Prometheus-Pandora observing
    campaign. The data for those satellites is also included in this
    data set.
 
 
  Observation summary and conditions
  ==================================
    For this investigation the primary new observations are from the
    ongoing HST WFPC2 campaign to observe the main rings of Saturn
    over the full range of ring tilt and phase angles visible from the
    Earth (1996-2002). These observations were made near opposition
    and quadrature. For completeness, HST WFPC2 archival observations
    of Saturn's rings taken in 1994-1995 were also used. The overall
    quality of the images used is excellent.
 
 
  Processing
  ==========
 
    See FRENCHETAL2003.
 
 
  Data
  ====
    The data provided here are in ASCII tables.  For each data file, a
    detached PDS label is provided containing additional information.
 
    Most users will prefer to focus on the PDS compliant data files in
    the DATA/EASYDATA/ subdirectory. These files and their labels
    contain all of the information in the original files provided by
    R. French. The original files are included for completeness and
    can be found in the DATA/SORCDATA/ subdirectory.
 
    The satellites for which data are included in this volume are:
    Dione, Enceladus, Epimetheus, Helene, Hyperion, Janus, Mimas,
    Pandora, Prometheus, Rhea, and Tethys.
 
    Satellite positions have been determined and are recorded in the
    individual table files by satellite. The data include the WFPC2
    image name, the midpoint UTC time of the observation, the arcsec
    offsets from the center of the planet (RA*Cos(Dec) and DEC, with
    their corresponding formal uncertainties. Details of the
    observations and reduction techniques may be found in
    FRENCHETAL2003.
 
  Ancillary Data
  ==============
    Calibration data is not provided. SPICE SPK files containing
    ephemeris information for the HST during the period covered
    by this data set are included in the SPICE/ directory.
 
  Coordinate System
  =================
    All geometric quantities appearing in the labels are in J2000
    coordinates.  In this coordinate frame, the z-axis points
    northward along the Earth's J2000 rotation axis and the x-axis
    points toward the First Point of Aries.
 
    All of the calculations are geocentric rather than 'HST-centric'.
    During peer review, Dr M. Evans noted this turns out to be a minor
    issue. He performed orbit fits to the Prometheus data. The
    resulting elements were effectivly the same whether using HST or
    the center of the Earth as the observation point. The differences
    in the derived orbital elements were much smaller than the
    associated errors.

Confidence Level Overview
  =========================
    High.
 
  Review
  ======
    These data completed peer review on August 13, 2004. Members of
    the peer review panel were: Nick Cooper (Queen Mary, University of
    London), Luke Dones (South west Research Institute, Mike Evans
    (Queen Mary, University of London), Richard French(Wellesley
    College), Robert Jacobson (JPL), and Carl Murray (Queen Mary,
    University of London).